Effect of extra carbon addition on the self-propagation high-temperature synthesis characteristics of WO3-H3BO3-Mg-C system

Abstract In this study, the self-propagating high-temperature synthesis characteristics of the WO 3 -2H 3 BO 3 -9Mg-(2 + x )C system containing various extra carbon contents (0 ≤ x ≤ 7) were investigated. X-ray diffraction analysis results showed that W, W 2 B, WB and small amounts of W 2 B 5 remained after acid leaching of the combustion products obtained using stoichiometric composition ( x = 0). The addition of extra carbon to the reactants did not result in the formation of a new phase. However, it changed the relative concentration of tungsten borides in the final composites in such a way that the boron-rich borides, like W 2 B 5 and WB, were the dominant phases at higher carbon contents. Moreover, the combustion front velocity and the adiabatic temperature of the system decreased with increasing the extra carbon molar concentration. Thermodynamic data along with the simultaneous thermal analysis were used to interpret the results. Furthermore, microstructure analyses showed that a powder composite with the nearly uniform distribution of various phases was formed. Moreover, the addition of extra carbon decreased the particle size of the products and led to the formation of tungsten borides nanoparticles.